Fix ps2toserial build.

* Share relevant stuff in common.mk so I don't have to repeat myself too much and copypaste all the time.
* Prepare for MCU switchability.


git-svn-id: svn://pulkomandy.tk/avrstuff@103 c6672c3c-f6b6-47f9-9001-1fd6b12fecbe
4 files changed